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EC number: 204-066-3
CAS number: 115-11-7
[14C]Isobutene at End of Exposure (as % of Total Body Burden mean ± SE,
n = 4)
Exposure concentration of isobutene
80.0 ± 0.6
0.87 ± 0.29
7.6 ± 0.2
6.4 ± 0.5
5.1 ± 0.2
F344/N rats were exposed to isobutene (2-methylpropene) by inhalation at
concentrations from 40 to 4000 ppm (91.8 to 918 mg/m3). A
time-course evaluation of blood levels of isobutene was performed and
urinary metabolites were determined. Blood levels of isobutene were
linearly related to exposure up to 400ppm (918 mg/m3) but were
supralinear at 4000 ppm (9180 mg/m3) indicating saturation of metabolism
at this higher dose level. Absorption of inhaled isobutene was about 8%
up to 40ppm but decreased at higher concentrations. At 40 ppm, over 90%
of absorbed isobutene was metabolised but at 4000 ppm 20% was excreted
as unchanged isobutene also indicating saturation of metabolism. Two
urinary metabolites were identified as isobutenediol and
2-hydroxyisobutyric acid. Two other urinary metabolites were tentatively
identified as sulfate conjugates of isobutenediol.
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